Surface K and surface H

This week we need to grind the surface H and surface K as shown in the diagram above. It was more really challenging. To do so, we put the work piece on the platform of the machine with 3 square blocks, acting as a support to the work piece. This was to prevent the work piece from flying away during the grinding process as the surface of the work piece that was in contact with the platform was too small, so it was not very stable when being magnetised on the platform. After that, we placed the grinding wheel very close to the surface K but it must not touch the surface k and tightened the knob that control the y-axis. This is also the main difference between the technique we learned in the previous week and this week. Normally, we will move the y-axis, so that all the surface is well ground but now due the small surface, but now we need not move the y-axis and just keep the x-axis moving. Then, we started grinding. First, we only ground 20 to 30 microns. This is to clean the the surface in order to make sure that the surface is flat before we could take an accurate measurement and grind to the dimension required. When the required dimension was reached, the value of z-axis was then reset to zero. Without moving the y-axis, the work piece was turned to the other site to be ground in the same way. At this time, we need not measure the workpiece again, we could just grind to the zero value of the z-axis that we had reset earlier. In such way, we could make sure that both side had equal height.

Square grinding

Last week, we only learned how to grind parallel surfaces of the work piece, that are the 2 T surfaces of the work piece.

This week, we learned how to grind all six surfaces of a the work piece. This technique is known as square grinding. There are more things need to take into consideration when to grind it into a square. Other than smooth and flat surfaces, we also need to grind all the surfaces into 90 degree to each other. To do this, we learned how to use a clamp. This clamp has an accurate of 90 degrees at the edge, so when the work piece is clamped on it and being ground, for sure, the work piece produced is also in 90 degrees.

Getting started

This week we get our own work piece, it looks like a T shape as shown in the photo above.

First, Mr Teng demonstrated to us how to dress the grinding wheel. It is an important process in order to produce a flat and smooth surfaces on the work piece. Before placing the diamond, which is used to dress the grinding wheel on the magnetic table, the table and the diamond must be cleaned. This is because tiny dust and dirt can also cause the grinding wheel is not well dressed. Then, the magnetised switch was on to magnetise the diamond so that it will not fly out when dressing. The x-axis remain stationary and the y-axis moves forwards and backwards manually to dress the wheel.The work piece can only start to be ground after the grinding wheel had been dressed.

Similarly, Mr Teng did the same thing as when dressing the grinding wheel when grinding the work piece. But there is one thing different from dressing the wheel, that is when grinding a work piece, the x-axis was set into automatic mode, it moved continuously throughout the grinding process.After Mr Teng demonstrated all steps, it was our turn to use the machines. But I was soon confused by the difference between the dressing process and the grinding process. I set the x-axis into automatic mode when dressing the wheel. Luckily, Mr Teng discovered and stopped me before any accident happened.

Parts of grinding machine

First, I would like to talk about few structures and parts of the grinding machine, so that it is clearer and easier for me to further continue my blog. There are 3 main axes, x-axis, y-axis and z-axis. Different axes are controlled separately by different wheel. X-axis is to move the working table or also known as magnetic table left and right. X-axis can be controlled manually and automatically. Automatic mode is more common to be used when grinding a work piece, so that the work piece is moving horizontally continuosly throughout the grinding process. While y-axis is to move the magnetic table towards or away from the users. The z-axis moves the grinding wheel vertically, nearer to the magnetic table or away from it. Each and every axis plays an important role in grinding a work piece. And the magnetic table is the place to place the work piece while grinding. It works base on the principle of electromagnetism. So, it can be magnetised and also demagnetised. Because most of the work pieces are made in steel, so it can be hold firmly on the magnetic table when the table is being magnetised, while we want to remove the work piece from the table, we just need to press the demagnetised button, then the work piece can be removed easily. And the most important part of this machine is the grinding wheel. It is harder than a steel. And due to this characteristic, it can cut the work piece which is usually made of steel without being damaged. However, when cut too deep, the wheel might be damaged or even crashed into 2 pieces. Also, to get a good finishing of the work piece, the grinding wheel need to be dressed using an industrial diamond. Following the same characteristic, diamond is harder than the grinding wheel, so diamond can be used to dress the wheel. Above is the photo of the grinding machine that we are going to use.